1. Field of the Invention
The present invention relates to switching technology for transferring data in a network.
2. Description of the Related Art
In a network switch, switching of a packet to the external device as the packet destination is performed by transferring a packet received from an external device connected to an input port to an output port specified based on the destination contained in the packet. In order to perform transfer of data between the input port and the output port at a higher speed, certain network switch uses a plurality of crossbar switches for transferring data from a receiving side transfer device with the input port to a transmitting side transfer device with the output port. With the network switch using the crossbar switches, typically, the received packet is divided into cells of a specified data length, and the divided cells are transferred by the plurality of crossbar switches.
In the case that the cells divided from the packet are transferred by the plurality of crossbar switches, the arrival sequence to the transmitting side transfer device of the cells that are transmitted through mutually different crossbar switches does not always match the transfer sequence to the crossbar switches from the receiving side transfer device. When the cell arrival sequence is not guaranteed, there is a case that the packet is not able to be properly restored from the cells due to incorrect cell sequence. In light of this, a conventional network switch sets serial numbers for each cell destination (CSN: cell serial number) of the crossbar switches at the receiving side transfer device, and cells are sorted in CSN sequence with a sorting process at the transmitting side transfer device.
However, if a CSN is set for each cell destination, as the number of transmitting side transfer devices increases, the number of circuits such as CSN setting circuits for setting the CSN increases. This causes increase of circuit scale of the network switch. In particular, when performing multicast transfer for transferring single cells to a plurality of transmitting side transfer devices at the crossbar switches, the number of circuits such as CSN setting circuits increases rapidly in accordance with the increase in the transmitting side transfer devices. This problem is not limited to when dividing a packet into cells and transferring the divided cells, but is common where it is required to maintain the transfer sequence of the unit data such as packets, cells and so on.